1. Field of the Invention
The present invention relates to mat materials, exhaust gas treating apparatuses, and mufflers.
2. Discussion of the Background
The number of automobiles has drastically increased since the turn of the century, and the amount of exhaust gas emissions from the internal combustion engines of automobiles shows no sign of slowing. Particularly, various substances contained in diesel engine exhaust gases are a major cause of pollution and seriously affecting the global environment.
Under such circumstances, various exhaust gas treating apparatuses have been proposed and put to practical use. A typical exhaust gas treating apparatus comprises an exhaust gas treating member having a number of fine openings which is installed in a casing (such as a metal shell) disposed at a location on exhaust piping connected to the engine exhaust gas manifold. Examples of such an exhaust gas treating member include a catalyst supporter (catalytic converter) and a diesel particulate filter (DPF). In the case of a DPF, fine particles are trapped by the surrounding walls of the openings in the aforementioned structure as the exhaust gas passes through the exhaust gas treating member, thus removing the fine particles from the exhaust gas. The constituent material of the exhaust gas treating member includes ceramics as well as metals and alloys. A well-known example of a ceramic exhaust gas treating member is a honeycomb filter made of cordierite. In recent years, porous sintered silicon carbide has been often used as an exhaust gas treating member material from the viewpoint of heat resistance, mechanical strength, and chemical stability.
Normally, between such an exhaust gas treating member and the casing, a retaining/sealing material is installed. The retaining/sealing material is used to prevent damage due to a contact between the exhaust gas treating member and the casing during the running of the vehicle. It is also used to prevent leakage of exhaust gas through a gap between the casing and the exhaust gas treating member. The retaining/sealing material also has the function of preventing the exhaust gas treating member from falling off due to the exhaust pressure of exhaust gas. Furthermore, since the exhaust gas treating member needs to be maintained at a high temperature in order to maintain reactivity, a good heat-insulating property is required in the retaining/sealing material. One example of material that satisfies these requirements is a mat material consisting of an inorganic fiber such as an alumina-based fiber.
Such a mat material is wound around at least a part of the external circumferential surfaces of the exhaust gas treating member except for its opening surfaces, and integrally affixed to the exhaust gas treating member by taping, for example. Thereafter, the integrated component is installed inside a casing by press-fitting or otherwise, thereby forming an exhaust gas treating apparatus.
Generally, the manufacturing process for the aforementioned mat material involves a needling treatment, which is a process of making a mat material thinner by putting a needle into and out of the mat material. The process causes the inorganic fibers to become woven in the thickness direction of the mat material while the thickness of the mat material is reduced. In this way, the loft of the mat material can be reduced (see Japanese Laid-Open Patent Application No. 07-286514, for example). The contents of Japanese Laid-Open Patent Application No. 07-286514 are incorporated herein by reference in their entirety.